My quick review.....
Let me start out with single player. The AI is decent, but there are the "let me stand in your line of fire", "let me heal you in a zombie horde" quirks. I will give the bots credit for good aim, especially when it comes to special zombies. On average, they also respond quicker when you get pinned down by zombies. Single player is doable, but this game was made for coop.
I'm giving valve credit for designing a solid survival horror coop game. You need to think strategically, as in choke points, and defensive rooftops. I really enjoy the times where you need to rush through an endless zombie to reach an objective. Melee is especially effective/gratifying during these rushes. Your arsenal is standard m16s, uzis, combat shotguns, the occasional grenade launcher, etc. If you're a gun-nut, Borderlands might be more your style. A bit of creativity with melee: frying pans, cricket bats, and (my favorite) the guitar, to name a few.
Graphics are great. They really captured the grit of the dirty south.
Soundtrack really fits the locale, but I wish there was more of it.
Let me get to my personal favorite part of the game, the online play. You can easily find a group to do a coop campaign with.
Most might be annoyed, but I enjoy how people's snap decisions affect gameplay. You might have a knowledgeable dude who makes the game fun. You also wenches who abandon the group while you stay back to protect a near-dead teammate. Then when you're ever so close, the wench escapes with the teammate you just saved, while you and another guy held down the fort. Swap dude with wench, if you prefer. That being said, GET A MIC , IT HELPS^1000. Typing in caps won't help when a zombie is pinning you down and your team is trying to sprint through a zombie horde. You can replay different chapters of the game, each about 1:30-2hrs, so you can replay it again with a better group. Just friend the better players in your group for future reference.
Here's my biggest grievance. I hate 'falling' off a ledges. You basically need someone to pull you up. Why you can't do it yourself, no matter how slow it takes, is lame. I "fell off" a ledge 10 ft from the ground and my teammate was pinned down.
Lame.
Versus mode is fun, especially when you're the infected. Teamwork is essential, more so then Team Fortress 2 even.
You might be able to do a little damage by yourself, but when you strangle a survivor in a pool of acid your buddy just puked up, well that's just beautiful teamwork.
In closing, if you like zombies, tactical thinking, gore of any combination of the above. Stop listening to the scrubs and get this.